Racing is known to severely load driveline components, including transmissions, drive shafts, differentials, and axles, of competing automobiles. In particular, drag-type racing, including all racing in which the competing automobiles accelerate at or near the automobile's maximum capacity during some or all of the race, imposes exceptionally severe loads on the drivelines. In this type of racing, maintaining the maximum acceleration the automobile can achieve and beginning to accelerate within an extremely short time is critical to success. To maintain maximum acceleration, the automobile's engine must be operated at or near its maximum power and that power must be continuously transmitted through the automobile's driveline.
Various types of racing automobiles having engines generating a range of horsepower from several hundred horsepower to several thousand horsepower compete in drag-type racing. The driveline components used with the various types of automobiles are adapted to transmit the power expected to be generated by the particular type of engine used by the automobile and for the particular type of race. A racing automobile having a high horsepower engine and competing in a short race requires an extremely strong driveline and may not require a transmission while an automobile with a lower horsepower engine does not require as strong a driveline and may use a two, three, or four speed transmission. Transmissions used in drag-type racing must reliably change gear ratios with a minimum interruption in power transmitted through the driveline. The combined requirements of transmitting high loads and minimum interruption of power during gear changes restrict the types of transmissions that can be used in drag-type racing.
Engines conventionally used in automobiles that compete in drag-type races generate their maximum power when operating at relatively high speeds. The engine must be disengaged from the driveline for the car to remain at a complete stop and the engine operate at or near its highest power. Clutches or fluid coupling torque converters mounted to the engine are used to apply power to a stopped or slowly rotating driveline from an engine operating at a high speed. The performance of the clutch or torque converter is critical to the performance of an automobile competing in drag-type racing, particularly at the start of the race.
Automobiles having engines producing the highest horsepower naturally require the strongest driveline components. Additionally, drivelines used with the highest horsepower engines must provide for adjustment of the rate at which power is applied through the driveline. This adjustment is conventionally provided through use of an adjustable clutch. Adjustable clutches having a significant range of adjustment are used in the highest horsepower cars for drag racing where it is critical that tires not be allowed to slip on the track surface. An adjustable clutch applies torque from an engine rotating at a high speed to a stationary or slowly moving output shaft by frictional sliding of plates within the clutch. The torque that is applied to the output shaft depends on the frictional characteristics of the clutch which may change due to clutch surface conditions, temperature, wear and other factors.
Automatic transmissions manufactured to be coupled with a torque converter in passengers cars were modified and adapted to be coupled to adjustable clutches in high horsepower racing automobiles at least twenty years ago. Breakage was a significant problem despite the use of strengthened transmission components. As high horsepower engines developed increased horsepower, these modified transmissions were found not to be able to withstand the higher horsepower. Transmissions are now manufactured specifically for use in the higher horsepower acceleration type racing. These transmissions have extremely strong gears, shafts and other components to withstand the severe loads. Planetary gear transmissions, such as those manufactured by Lenco, Inc. are now commonly used in drag-type racing by cars using the highest horsepower engines. Because these transmissions are made specifically for use with higher horsepower engines, they are conventionally used with an adjustable clutch.
Automobiles constructed for drag-type racing having lower horsepower engines conventionally use automatic transmissions to increase the mechanical advantage of the engine and provide reliable gear changes. These automatic transmissions are typically transmissions that were originally manufactured for use in a passenger automobile and that have been modified by replacing production parts with strengthened components. Automatic transmissions modified for lower horsepower racing are now typically coupled to the engine by a torque converter, similar to those used with the transmission in passenger automobiles. These racing torque converters are designed to operate with transmission fluid supplied from the transmission pump that provides fluid to operate the automatic transmission. Several manufacturers have developed torque converters that enhance the performance of automobiles using various automatic transmissions for drag-type racing. Automatic transmissions manufactured for conventional automobiles that are strengthened and modified for racing are significantly less expensive than racing transmissions that are manufactured for use with the highest horsepower engines.
Drag racing by lower horsepower automobiles often requires that competing automobiles finish the race in a time that is not less than a specified time. Automobiles engaging in that type of racing are positioned at a starting line and begin the race when a signal is given. Because the time in which the automobile may complete the race can be no less than a specified time, beginning the race quickly becomes extremely critical. Reaction of both the driver to the start signal and the automobile to the driver are critical.
Torque converters are recognized as best suited for racing in which applying power to the drive train in the shortest possible time is critical and in which a large range of driveline adjustment is not required. The output shaft of a torque converter may be stopped while the throttle of the engine to which the torque converter is connected is fully open. The output shaft may be stopped by applying the automobile's brakes or otherwise restraining driveline motion. A racing torque converter having the output shaft stopped will not allow the engine to rotate faster than a "stall speed." At the stall speed, the engine applies a torque through the torque converter to the stopped output shaft of the torque converter. That torque is determined by the power of the engine at the stall speed and the characteristics of the torque converter. Upon disengagement of the output shaft restraint, torque applied to the driveline by the torque converter accelerates the automobile. Power is quickly and predictably applied to the driveline when the output shaft restraint is released.
As now used in racing automobiles, torque converter characteristics are not adjustable. To change stall speed or other torque converter characteristics, the torque converter must be replaced. Difficulty in adjusting torque converters may impair an automobile's performance by precluding adjustments that may optimize the automobile's performance. This difficulty is generally considered to be outweighed by the advantages offered by a torque converter for racing automobiles having lower horsepower engines. The weight of such automobiles and the availability of tires providing increased traction to prevent slipping make these racing automobiles require less driveline adjustment than higher power racing automobiles. For racing automobiles using lower horsepower engines, the advantages of reliable and responsive performance offered by a torque converter outweigh the limitation on adjustment.
Despite the use of strengthened driveline components, the physical restrictions of the original design of an automatic transmission limit the modifications that can be made to withstand racing loads. Similar to the experience in racing automobiles using higher horsepower engines, racing automobiles that now typically use modified automatic transmissions are producing greater horsepower and the number of races that the modified automatic transmission can withstand before failure of the transmission can be very small. A race may be lost as a result of transmission failure. If the failure does not cause the racing automobile to lose the race, the transmission must be repaired or replaced before the automobile can race again. As a result, the automatic transmission of a racing automobile competing in an event consisting of a series of elimination races may be replaced several times during the event. The cost of using modified automatic transmissions is increased proportionally to the number of transmissions required.
The need therefore exists for a torque converter driven transmission that will withstand the severe loads imposed by drag-type racing. In addition, the need also exists to provide for convenient adjustment of the torque transmission characteristics of torque converters installed in racing automobiles. In drag racing, in particular, a reliable fast-release brake is required for a torque converter driven driveline to provide reliable restraint of the driveline before the race begins and the fastest possible release of the driveline to begin racing.